Novelist Quinn Dalton discusses the dangers of unbylined reviews:

There are some good arguments to be made for trade publications reviewing books anonymously. Nobody wants to read a review that is a thinly-veiled tool for self-advancement or a little back-slapping between friends. But anonymity causes as many problems as it solves, and I think reviewers-at least the professionals-—should cut it out...

...Why does Amazon want customers to attach their names to their reviews? As Jerome Weeks, books editor of the Dallas Morning News, put it in a 2004 article "Book Blurbs But No Names? For Shame," which discussed the Amazon glitch, "The real question is the implied moral challenge: Who are you to pass judgment on books?"

Weeks then makes a distinction between the consumer and professional reviewer. "Any reader will have his own opinions and can express them freely on Amazon. The more, the merrier (although it certainly helps if you can spell). But, contrary to popular belief, a review is not simply an opinion. A review is an act of persuasion, an argument."

And, he wonders, "Who knows what ax an anonymous critic may be grinding?"

More here.